Showing papers in "Russian Journal of Non-ferrous Metals in 2021"

Microstructure and Mechanical Effects of Co–Ti Powder Particles on Cu Matrix Composites

Abstract: Powder metallurgy was used in this study. High purity cobalt and titanium powders were added to copper powders at a ratio of 5–10–15 wt %. The reinforcing powders added to the copper powders were mixed for about 6 hours in a Turbula device. Then, the powders were compressed by applying 600 MPa using a hydraulic press. The samples were sintered at 1000°C for 30 min. After sintering, density measurements, and microstructure and mechanical tests of the samples were done. Scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction analyses were performed in the microstructure characterization. Tensile and wear analyses were performed for mechanical experiments. The tensile test results were determined by applying certain loads to the samples. The tensile strength of the 5 wt % Co–Ti reinforced sample was the highest, with an average of 118.65 MPa, and the ductility increased in parallel. Weight loss, friction coefficient change, and wear diameter image results were obtained from the wear test. The lowest weight loss was observed in the composite containing 5 wt % Co–Ti and this value was determined as 0.0191 g. The increase in the reinforcement rate contributed positively to tensile and abrasion resistance.

Issues and Requirements for Aluminum Alloys Used in Aircraft Components: State of the Art

Abstract: Aluminum alloys have always been the material of choice for the aircraft industry owing to their versatile attributes, such as excellent strength to weight ratio, good corrosion resistance, thermal conductivity, and low production cost after wood. However, these days composite materials, carbon fiber reinforced plastic and fiber metal laminate are substituting aluminum alloys mainly because of their incapability to work at high temperatures. Nonetheless, continuous research in these aluminum alloys will effectively combat with those modern polymer composites and carbon fiber reinforced plastic. And so forth, mechanical and tribological properties of aluminum alloys can nowadays be enhanced by adding a suitable reinforcement in an appropriate volume fraction. Reinforcements like micro or nano sized SiC, Al2O3, TiC, B4C, SiO2 and iron powder when used, can alter the microstructural characteristics that develop excellent physical and mechanical properties in aluminum alloys, primarily for aerospace applications. These alloys are being used in different aircraft components that have a relative motion, like actuators and track roll units of a control surface. Stress and wear are generated due to the relative motion of these components during take-off and landing, causing a rise in temperature. And hence, a brief study on moving components used in aircrafts and tribological behaviour of aircraft components is presented in the literature. Also considering that the selection of an appropriate material for the proper functioning of an aircraft component is critical, three most important properties viz. strength, fatigue and corrosion resistance of an aircraft have been provided. Therefore this review article emphasizes on the following topics: (1) aluminum alloys in the aerospace industries, (2) aircraft components with relative motion, their working and material being used, (3) substantial properties of aircraft components viz. strength, fatigue resistance and corrosion resistance, (4) tribological aspect of an aircraft, (5) elevated-temperature behaviour of aluminum alloys, and (6) role of reinforcement for improving properties. This review article is beneficial for those researchers and academicians who want to seek the understanding, pertaining to the usefulness of the aluminum in the aircraft industry.

Effect of Deep Cryogenic Treatment on Wear and Corrosion Resistance of an Al–Zn–Mg–Cu Alloy

Abstract: The 7075 aluminum alloy was subjected to deep cryogenic treatment (DCT) at –196°C with liquid nitrogen for different hours. The wear and corrosion behaviors of the alloy were investigated by hardness, friction and wear, intergranular corrosion (IGC), and electrochemical corrosion tests. The microstructure of the alloy was observed by transmission electron microscope (TEM). The results showed that both the wear and corrosion resistance of the alloy treated with DCT could be improved. After the DCT 12 h, the matrix precipitates of the alloy were fine and homogeneously distributed, and the grain boundary precipitates of the alloy were discontinued, so that the alloy performed better comprehensive properties.

Actual Trends in the Application of Rare-Earth Metals and Their Compounds in the Production of Magnetic and Luminescent Materials: A Review

Abstract: Current trends in the application of rare-earth metals (REMs) in two major scientific and technological fields—the production of magnetic and luminescent materials—are considered. It is shown that it is REMs that endow these products with unique properties. The information on the content of the matrix and doping components and their influence on achieving the required characteristics of the most popular magnetic materials is systematized. The potential of new combinations of REMs for further progress in the production of magnetic materials for various purposes is described. Along with the traditional cobalt–samarium and neodymium–iron–boron compositions, new magnetic materials with increased hysteresis properties and better time–temperature stability are developed, and phases with variable valence, used as memory elements in information systems, are synthesized. In addition, the article also reviews and summarizes the results of studies in the creation of luminescent materials, which is another important area of application of REMs. Phosphors based on compounds of REMs are used in the production of high-pressure mercury lamps with improved characteristics, X-ray screens, high- and low-pressure fluorescent lamps, and screens for electrooptical converters. Narrow-band phosphors based on REM compounds are of interest for lamps used for growing plants, especially in areas with a cold climate, where growing plants year-round is possible only with the use of additional radiation sources. The trends in the synthesis of luminescent materials with varied REMs and their combinations are revealed. Emphasis is placed on the need to use chemically pure REM precursors in the synthesis of such materials. The prospects for the creation of nanophosphors, as well as the improvement of methods of synthesis and diagnostic techniques, are noted.

Investigation of the Stress-Strain State and Microstructure Transformation of Electrotechnical Copper Buses in the Deformation Zone during Continuous Extrusion

Abstract: A comprehensive study of the features of physical and mechanical processes occurring in the deformation zone of metal during continuous extrusion is carried out with rectangular Cu-ETP buses 10 × 60 mm in size. With the use of finite element computer simulation, values of the power parameters of the extrusion process are obtained. It is noted that the values of the torque and force increase until the free space of the press chamber is filled with metal, reaching maxima of 12.26 kN m and 1.54 MN, respectively. As a result of an analysis of the stress-strain state of metal in the deformation zone, the fields of distribution of equivalent strain, strain rate intensity, and average stresses are obtained and the graph of change in the metal temperature with the time of the extrusion process is plotted. The maximum of the equivalent strain and compressive stresses are observed in the region of contact between the workpiece and the abutment of the press container. That is also where the most intense deformation-induced heating of the metal occurs. A comparison of the results of modeling and microstructural studies indicates that a significant part of work on refining the cast structure takes place at the entrance to the deformation zone and in the abutment region, where the level of compressive stresses is the highest. Plastic deformation of the metal passing through the die leads to the formation of an oriented crystal structure with a grain size of 25 to 30 µm. The results of measuring the hardness of the samples are very consistent with the results of analyzing the structure in the studied regions of the deformation zone. When the workpiece passes through the abutment region of the press container, deformation-induced heating occurs, which leads to a decrease in the hardness from 93 to 67 HV. After the metal passes through the die, recrystallization processes continue in it, leading to a slight increase in grain size and, accordingly, a decrease in the hardness from 79 to 74 HV, which lasts until the bus comes into contact with a cooling medium.

Grain Refinement of Casting Aluminum Alloys of the Al–Mg–Si System by Processing the Liquid Phase Using Nanosecond Electromagnetic Pulses

Abstract: In this paper, using the AA 511 alloy of the Al–Mg–Si system as an example, it is shown that the irradiation of aluminum melts with nanosecond electromagnetic pulses (NEPs) leads to a significant change in the nature of structure formation during crystallization, contributing to the refinement of the structural components of the alloy and the redistribution of alloying elements in them. It has been established that an increase in the frequency of irradiation of NEP melts is accompanied by the refinement of the structural components of the alloy, while the greatest degree of decrease in the grain size of the α-solid solution and intergranular inclusions of the eutectic Mg2Si phase is observed at an NEP frequency of 1000 Hz. An increase in the NEP frequency leads to a significant increase in the concentration of magnesium in the α-solid solution and the fragmentation of intergranular inclusions of the Mg2Si phase, which, when the melt is irradiated at a frequency of 1000 Hz, is released in the form of compact isolated inclusions. The processing of melts with NEPs leads to an increase in the Brinell hardness of the specimens in the cast state, as well as to a significant increase in the microhardness of the grains of the α-solid solution (from 38.21 in the initial state to 61.85 HV 0.001 after irradiation with a frequency of 1000 Hz). It is assumed that the effect of a pulsed electromagnetic field leads to a decrease in the critical values of the Gibbs free energy required to initiate nucleation processes and to a decrease in the surface tension at the “growing crystal–metal melt” interface, which causes a modifying effect on the alloy structure due to a decrease in the critical size nuclei of crystallization.

Influence of Melt Superheating Treatment on the Cast Structure of Al–Sn Alloys

Abstract: In this article, the effect of melt superheating treatment (MST) for Al–Sn alloys has been studied. To determine the optimal superheat temperature, the authors measured the temperature dependences of the kinematic viscosity, electrical resistivity, density, and surface tension of Al–Sn melts with tin contents of 10, 20, 30, 40, and 50 wt %. According to the measurement results, temperature t* is determined for each Al–Sn alloy; upon heating to that point, the micro-inhomogeneous state is destroyed and the heterogeneous liquid–homogeneous liquid structural transition occurs. MST results in a decrease in melt viscosity. It is found that temperature t* rises with an increasing tin concentration in the Al–Sn melt. An increase in the tin content in the Al–Sn melt also leads to a decrease in the absolute values of the kinematic viscosity and surface tension, while the electrical resistivity and density increase accordingly. Thus, the MST mode for Al–Sn alloys was determined. The effect of MST of the Al–Sn 50 wt % melt on the microstructure and mechanical properties of the ingot is studied. It is necessary to determine the structural sensitivity to the degree of overheating of the melts and find a new strategy to improve the shaping ability of the two-phase structure of Al–Sn alloys. The results show that the method of resistivity and viscosity are more sensitive and effective for determining the temperature of the superheat of the melt (MST mode). In addition, the desired modified Al–Sn ingot structure can be formed under normal casting conditions; MST can contribute to the formation of a modified ingot structure by increasing the solidification time and decreasing the average solidification rate by reducing the melt viscosity after superheating.

Production of WC–15Co Ultrafine-Grained Hard Alloy from Powder Obtained by the Electroerosive Dispersion of VK15 Alloy Wastes in Water

Abstract: In this paper we study the possibility of producing a WC–15Co ultrafine-grained hard alloy (HA) from a powder obtained by the electroerosive dispersion (EED) of wastes of a VK15 HA in water. As a result of the EED of the alloy in the oxygen-containing liquid, the carbon concentration in the resulting powder decreases from 5.3 to 2.3%. When the powder is heated to 900°C in a vacuum, the carbon content drops to 0.2% due to the presence of oxygen. The resulting powder includes WC, W2C, and Co phases. The particles have a dendritic structure consisting of newly formed tungsten-containing grains and cobalt interlayers. In this study, the controlled removal of oxygen and the replacement of carbon in the powder were performed under heating in a CO atmosphere to t = 900°C. The processed powder has the required phase composition (WC + Co) and contains 5.3% carbon. The particles retain their spherical shape after carbon replenishment. The WC grains in the particles acquire a lamellar configuration, the space between which is filled with cobalt. The average grain diameter was found to be smaller than that in the initial alloy. As a result of sintering the powder in vacuum at 1390°C, a WC–15Co ultrafine-grained HA is obtained, the average diameter of WC grains in which is 0.44 μm, which is several times smaller than that in the initial alloy (1.8 μm). In this case, most of the grains retain their lamellar shape. Due to the fineness and 15% cobalt content, the resulting alloy has high hardness (1620 HV), fracture toughness (13.2 MPa m1/2), and strength (1920 MPa). In terms of the set of characteristics, this material is not inferior to analogs obtained by other methods.

Enhancement of Tensile and Microhardness of AA 6082-T6 Friction Stir Welds via Brass Interlayers

Abstract: This paper investigates the effects of brass interlayer on the microstructural and mechanical properties of friction stir welded AA 6082-T6. To analyze the reaction and distribution of brass interlayer with the aluminum alloy in the stir zone, scanning electron microscopy (SEM) and optical microscopy were used. X‑ray diffraction (XRD) analysis was used to examine the phase composition. Tensile and microhardness testing was performed to investigate the mechanical properties. The results showed that with brass interlayer, the joint’s tensile strength increased to ~33% compared to joints without interlayer. The microstructural analysis indicated that the brass interlayer dispersed very well at the stir zone, which can be observed through the optical image. At the nugget zone, the mixing of brass with the aluminum matrix can be observed, which results in the formation of intermetallic compounds (IMCs). Fractography investigation of the fractured tensile specimen indicates pure ductile fracture in Al–Al joints shifted towards brittle fracture due to the formation of IMCs in the joints with a brass interlayer. In summary, it can be concluded that the use of brass interlayer is an effective way to overcome the softening issue in friction stir welding of similar aluminum alloys.

Structure and Mechanical Properties of Al–Ca–Mn–Fe–Zr–Sc Eutectic Aluminum Alloy after Warm Equal Channel Angular Pressing

Abstract: Recently developed multicomponent eutectic alloys based on Al–Ca are promising for practical application, since they are characterized by low density and high corrosion resistance and are hi-tech in casting and easily deformed in annealed state. These alloys are strengthened by alloying with Mn, Fe, Zr, Sc, and other elements. The ultrafine grained state in aluminum alloys is achieved by severe plastic deformations, for instance, equal channel angular pressing (ECAP), significantly improving their mechanical properties. In this regard, this work is aimed at analyzing the influence of warm ECAP on the structure, mechanical properties, and thermal stability of eutectic aluminum alloy, wt %: Al–3.5Ca–0.9Mn–0.5Fe–0.1Zr–0.1Sc. ECAP is performed on as-cast alloy specimens with a diameter of 20 mm (400°C, route BC, channel intersection angle: 110°, number of passes N = 6). It is been demonstrated that, as a consequence of ECAP, a developed substructure is generated in the alloy with a high density of dislocations and deposition of Al6(Mn, Fe) and Al3Sc nanosized particles, accompanied by the fragmentation of primary Al6(Mn, Fe) coarse particles and eutectic Al4Ca particles. Such a change in structure during ECAP leads to the significant strengthening of the alloy: its strength increased 1.5–2.0 times and relative elongation decreased 1.3 times in a specimen of longitudinal cross section, slightly changing in the transversal one in comparison with the initial state.

Recovery of Cobalt, Copper and Zinc from Küre-Kastamonu Historical Copper Slag by High Pressure Oxidative Acid Leaching

Abstract: Copper slags are solid by-products formed during the copper production process by pyrometallurgical method from sulfide copper ores. These slags usually contain significant quantities of valuable metals, such as cobalt, nickel, zinc and copper, in different forms. Extraction characteristics of Cu, Co, Zn, and Fe from Kure historical copper slag (KHS) by oxidative pressure leaching were investigated with sulfuric acid lixivant in this study. The phase composition of the studied slag was identified by the use of a combination of methods, including a mineral liberation analyzer (MLA), a scanning electron microscope coupled with an energy-dispersive spectrometer (SEM-EDS), and X-ray powder diffraction (XRD). Bornite, chalcopyrite, cuprospinel, brochantite, chalcocite, and metallic Cu are identified as copper-containing minerals. The samples used in leach tests contained averages of 0.84% Cu, 0.34% Co, 0.23% Zn, 2.90% Al, 0.70% Ca, 1.30% S, and 42.80% Fe. The factors affecting the performance and efficiency of the pressure leaching process, such as acid concentration, leaching time, solid/liquid ratio, oxygen partial pressure, particle size, and temperature, were investigated separately. It was found that metal extraction increased with temperature and sulfuric acid concentration. However, high acid concentrations led to gel formation that caused filtration problems. Under optimum conditions, the extraction efficiencies of cobalt, copper, and zinc from KHS were 96.82, 92.85, and 93.44%, respectively, while the extraction of iron was only 0.3%.

Experimental Investigation on the EBM-Based Additively Manufactured Prismatic Nickel–Titanium SMA Components

Abstract: Additive manufacturing (AM) of the nickel–titanium (NiTi) shape memory alloys (SMA) have provided novel component solutions with a variety of design configurations in the industry. Electron beam melting (EBM) is a trending metal additive manufacturing process for industrial applications in the field of biomedical and aerospace engineering. In this study, experimental investigations were conducted to reveal the effect of processing conditions on the microstructure and hardness properties of EBM-fabricated nickel-titanium components. Furthermore, detailed microstructural characterizations were performed with a scanning electron microscope, EDS, and XRD for unveiling of the microscopic structure and phase analysis during the layer by layer solidification. The experimental results were systematically evaluated for the powder and the bulk prismatic components, respectively.

Current Status of Copper-Ore Processing: A Review

Abstract: An analysis of flowsheets for processing sulfide and oxide copper ores, reagent modes, processing equipment, and flotation indicators in some domestic and foreign processing plants and productions is carried out. Autogenous and semiautogenous mills are commonly used in the primary grinding stage in ore processing plants, which excludes medium and fine crushing. The alternative is high-pressure grinding rolls, which can reduce electricity consumption compared with autogenous and semiautogenous grinding. An increase in the use of large-volume and high-performance ore-processing flotation equipment to maintain the quality and quantity of the product is noted. In addition to ball mills, fine- and ultra-fine-grinding mills in different configurations are widely used in the regrinding stage of the rougher flotation concentrate. An analysis of the flotation reagents to increase the efficiency of the separation process is made, where domestic and foreign approaches to the selection of flotation reagents are given. It should be noted that the combination of primary and secondary collectors is often used in foreign processing plants. Flotation reagents used in the processing of copper sulfide and oxide ores and their costs are presented. The combined circuit of flotation-hydrometallurgical processing of mixed copper ore at the Udokan deposit is considered. The conclusions reveal the current trends in the processing of copper ores, including the choice of equipment.

The Adsorption of Silver on Powdered Activated Carbon in the Ammonia-Free Thiosulfate Leaching Solution

Abstract: The ammonia-free thiosulfate extraction of silver can produce silver-copper polymetallic thiosulfate complex in leaching solution. Advanced processes for the recovery of silver in the leaching solution include adsorption, resin, or solvent extraction processes. In this work, the ability of powdered activated carbon (PAC) to adsorb silver in the ammonia-free thiosulfate solution was systematically studied at varying PAC mass (0.5–2.5 g), pH (6.04–11.66), silver concentration (500–1000 mg/L), thiosulfate concentration (0.01–0.1 mol/L), coexisting copper concentration (0–300 mg/L), temperature (298–318 K), and adsorption time (0–360 min). The adsorbent was well characterised by X-ray photoelectron spectroscopy (XPS). The results indicate that more than 92% of Ag(I) could be recovered over a wide pH range, and the adsorption capacity increased with adsorption temperature, reaching a maximum of 42 mg/g-PAC. Analysis of the adsorption isotherm and kinetics parameters indicate that the adsorption of Ag(I) on PAC is with Freundlich isotherm, and the adsorption follows pseudo-second order kinetics.

Ensuring Strength in Laser Welds Made Using the Dispersion-Hardened EP693 Nickel Alloy

Abstract: The process of making a weld using the heat-resistant EP693 alloy (Ni–Cr–W–Co–Co–Mo system) to make assemblies and components for gas-turbine engines (GTEs) is considered based on laser welding using a TruLaser Cell 7020 CO2 installation operating in the pulse-periodic radiation mode. EP367 (Ni–Mo–Cr–Mn) additive wire is used to obtain the weld. The effect of thermal treating is studied to estimate the change in structure and properties both in the weld-adjacent area and in the weld. The results are used to examine the structure of the weld and its breaks. The physics and mechanical properties of the weld are evaluated. The greatest durability limit is estimated for welds at a level of 2 × 106 cycles. The feasibility of using a laser-welding heat-resistant dispersion hardened nickel alloy is evaluated to make support and stator shells for GTEs. It is established that complex thermal treatment (quenching and aging) provides for the optimum values of strength at room temperature and at high temperatures. It is also responsible for the short-term strength of welds. According to the strength calculations made for the support and stator of GTE shells and experimental data, the strength of welds made using pulse-periodic laser welding results in a strength safety factor between 1.35 and 3. This technology is proposed for industrial application to make shell parts and assemblies to be used in GTE support and stator in order to improve the quality of welds with a reducing time of high-temperature heating to bring down power consumption.

Features of Structure Formation in an Al–Fe–Mn Alloy upon Crystallization with Various Cooling Rates

Abstract: Specific features of the microstructure formation of an Al–2.5% Fe–1.5% Mn alloy owing to the cooling rate during casting and during laser melting are studied in this work. An analysis of the microstructure in the molten state shows that, with an increase in the cooling rate during crystallization from 0.5 to 940 K/s, the primary crystallization of the Al6(Mn,Fe) phase is almost completely suppressed and the volume of the nonequilibrium eutectic increases to 43%. The microstructures of the Al–2.5% Fe–1.5% Mn alloy after laser melting are characterized by the presence of crystals of an aluminum matrix of a dendritic type with an average cell size of 0.56 μm, surrounded by an iron-manganese phase of eutectic origin with an average plate size of 0.28 μm. The primary crystallization of the Al6(Mn,Fe) phase is completely suppressed. The formation of such a microstructure occurs at cooling rates of 1.1 × 104–2.5 × 104 K/s, which corresponds to the cooling rates implemented in additive technologies. At the boundary between the track and the base metal and between the pulses, regions were revealed consisting of primary crystals of the Al6(Mn,Fe) phase formed by the epitaxial growth mechanism. The size of the primary crystals and the width of this zone depends on the size of the eutectic plates and the size of the dendritic cell located in the epitaxial layer. After laser melting, the Al–2.5% Fe–1.5% Mn alloy has a high hardness at room temperature (93 HV) and, after heating up to 300°C, it has a high thermal stability (85 HV). The calculated yield strength of the Al–2.5% Fe–1.5% Mn alloy after laser melting is 227 MPa. The combination of its ultrafine microstructure, high processibility during laser melting, hardness at room and elevated temperatures, and high calculated yield strength make the Al–2.5% Fe–1.5% Mn alloy a promising alloy for use in additive technologies.

Structure and Properties of EP741NP Heat-Resistant Nickel Alloy Produced by Selective Laser Melting

Abstract: The structure of EP741NP alloy samples produced by selective laser melting (SLM) in various technological modes, with various types of defects (the volume fraction of which varies from 0.31 to 0.65%), is investigated using optical and scanning electron microscopy; the mechanical characteristics of the samples are determined by tensile tests. All investigated SLM samples are typified by low strength characteristics, which is associated with the formation of a metastable single-phase structure, as well as with the presence of structural defects in the form of cracks. To improve the mechanical properties, the postprocessing of various types is carried out, including hot isostatic pressing (HIP); the heat treatment (HT) of the “quenching + ageing” type; and complex processing, which combines HIP and HT. According to the research results, the influence of various types of postprocessing on the microstructure and properties of SLM samples is determined. It is established that the use of HIP contributes to a decrease in porosity down to 0.04 vol %, the recrystallization of the structure, and the precipitation of the strengthening intermetallic phase based on Ni3Al (γ' phase) in the form of large particles of different sizes that create agglomerates. HT leads to the recrystallization of the structure and the precipitation of the finely dispersed γ' phase, which is uniformly distributed in the alloy matrix. In this case, the strength characteristics of the samples after HIP and HT are approximately on the same level (σu ~ 1250–1290 MPa); however, the ductility of the samples after HT is significantly lower, which is associated with the retention of defects in the structure in the form of cracks and large pores. The maximum increase in mechanical characteristics (σu of up to 1460 MPa and δ of up to 21.3%) is recorded during the complex postprocessing (HIP + HT), which ensures the elimination of defects and the formation of an optimal alloy structure.

Cerium Effect on the Phase Composition and Crystallization Behavior of Aluminum Casting Alloys Based on the Al–Mg–Si System

Abstract: Using a Thermo-Calc software package (TCAl4.0 database), unexplored data concerning the phase composition and crystallization behavior of Al–Mg–Si–Ce alloys have been obtained in the composition range of two-phase cast aluminum-magnesium alloys such as (Al) + Mg2Si. It is shown that phases such as (Al), Al4Ce, Mg2Si, and Al8Mg5 can form in the course of crystallization. At a concentration of Mg amounting to 4% and at a concentration of (Si + Сe) = 1.5%, a simultaneous increase in Ce and decrease in Si from 0.2 and 1.3%, respectively, allow consecutive reactions L + (Al) + Al4Ce and L + (Al) + Al4Ce + Mg2Si to occur. This makes it possible to propose that the Al4Ce phase can hinder the growth of the eutectic Mg2Si phase. Moreover, at a temperature of 20°С, such a change in concentrations decreases the amount of Mg2Si and increases the fraction of the Al8Mg5 phase, which is also accompanied by a decrease in the amount of magnesium silicide. When adding Ce in the Al–4% Ce–0.5% Si alloy, the fraction of Mg2Si is approximately constant throughout the entire crystallization range (1.34%), but each 0.1% of Ce results in a 0.17% increase in the fraction of the Ce-containing intermetallic compound, whereas, at 0.7% of Ce, the fractions of the two phases become equal. In studying the phase composition upon characteristic annealing-temperature values amounting to 400 and 550°С, it has been revealed that, due to the Al8Mg5 phase dissolving, the (Al) solid solution becomes supersaturated. Every 0.1% of Ce leads to a 0.005% increase in the Mg content in (Al) at 400°С and to a 0.01% increase in that at 500°С, which could indicate the potentialities of a positive Ce effect on matrix strengthening. Based on the results, it has been concluded that it is worthwhile to add Ce in an amount of up to 0.7%, which leads to slightly decreasing liquidus temperature (~636–638°С), but results in a 30°С decrease in the nonequilibrium solidus temperature to 421oС. At the same time, at a constant temperature of the Mg2Si phase formation (581°С), upon adding Ce, the crystallization range of the (Al) + Al4Ce eutectic expands, which can compensate for the deterioration of casting properties. The Al–4% of Ce–0.5% Si–0.7% Ce alloy has the following phase composition: Al4Ce 1.19%; ratio [Mg2Si/Al4Ce] = 0.89; and fraction of Al8Mg5 of 7.92% at 20°С and 3.22 and 3.36% Mg in (Al) at temperatures of 400 and 550°С, respectively. These results can be the basis for further experimental studies to justify the compositions and temperature modes required for obtaining aluminum-magnesium cast alloys containing Ce that exert a modifying effect on the eutectic Mg2Si inclusions.

Effect of the Cooling Rate on the Microstructure and Properties of C92900 Bronze

Abstract: In mechanical engineering, antifriction tin bronzes are used for manufacturing friction parts, for example, C92900 bronze, which is used on aircraft braking systems. One way to improve the properties of leaded tin bronzes is to increase the cooling rate during solidification. In this work, the effect of the cooling rate and the changes in the content of alloying elements within the limits established by industry standards on the properties of C92900 bronze are investigated. In order to provide different cooling rates, the alloys are casted into molds made of resin-bonded sand, steel, and graphite, for which the cooling rates were 0.4, 5, and 14.6°C/s. The influence of the cooling rate and the composition of bronze on the freezing range, macrostructure, microstructure, thermal conductivity, hardness, tensile properties, and wear rate are investigated. By means of differential thermal analysis, it is shown that upper limit alloying of C92900 bronze leads to a decrease in the solidus temperature by 40°C, which should be considered during deformation processing and heat treatment. An increase in the cooling rate during the solidification of C92900 bronze ingots provides a significant grain refinement and change in the amount, size, and morphology of the phases. For example, in the case of metallic and graphite mold casting, the size of the lead particles decreases and its circularity increases. The change in the Sn content within the range established by industrial standard has a significant effect on the intermetallic γ-(Cu, Ni)3Sn phase fraction. The increase in the cooling rate has no significant effect on the thermal conductivity of C92900 bronze, but it leads to an increase in hardness by 30 HB. It also improves the yield strength and ultimate tensile strength of the bronze. The wear test, carried out in accordance with the shaft–partial insert scheme in a kerosene medium using a steel counterbody, shows that an increase in the cooling rate during solidification leads to an increase in the wear rate of bronze from ~0.4 × 10–8 to ~1.2 × 10–8. The change in the bronze composition within the industrial standard range has practically no effect on the wear rate, but leads to a slight increase in the coefficient of friction.

Joint Metallothermic Reduction of Titanium and Rare Refractory Metals of Group V

Abstract: The features of phase formation during the joint aluminothermic reduction of titanium, niobium, tantalum, and vanadium from their oxides are studied using thermodynamic modeling and differential thermal (DTA) and X-ray diffraction phase analysis Using computer thermodynamic modeling made it possible to predict the optimal temperature conditions in the metallothermic process, the composition and ratio of the reagents in the charge, the behavior of the elements, and the sequence of the phase formation To identify the kinetic and thermochemical components of the process, thermodynamic calculations are supplemented by differential thermal studies using combined scanning calorimetry An analysis of the theoretical and experimental data shows that the interaction of aluminum with titanium dioxide proceeds through the stage of formation of titanium monoxide and results in the formation of TixAly intermetallic compounds of various compositions (TiAl3, TiAl, and Ti2Al) depending on the Al to TiO2 ratio in the batch When titanium dioxide is partially replaced by niobium, tantalum, and vanadium oxides, the metallothermic process under interactions in the Al–TiO2–Nb2O5, Al–TiO2–Ta2O5, and Al–TiO2–V2O5 systems is of the similar character; enters the active phase after the formation of liquid aluminum; is accompanied by exothermic effects; and is characterized by the priority formation of titanium aluminides and binary and ternary intermetallic aluminum compounds with rare refractory metals of group V such as AlNb3, Al3Nb, Al3Ta, Al3(Ti1 – х,Taх), Al3(Ti,Ta), and Al3(Ti08V02) The joint conversion of titanium dioxide and rare refractory metal pentoxides during the reduction process is affected through sequential and parallel stages of the formation of simple and complex element oxides with low oxidation states

Studies on the Fracture Mechanism for an Al–Al4C3–Al2O3 Aluminum-Matrix Dispersion-Hardened Composite with a Layered Structure under Static and Impact Loading

Abstract: Aluminum-matrix dispersion-hardened composites are widely used in engineering owing to the combination of high strength characteristics and low density, which makes it possible to create lightweight and fracture-resistant structural elements for different purposes. They are used for the manufacture of abrasive, tribotechnical products; piston-block parts for internal combustion engines; airframes; and other special products. This work is aimed at studies concerning the fracture mechanism for layered dispersion-hardened Al–Al2O3–Al4C3 composites under the conditions of static and impact loading obtained using the liquid-phase vacuum sintering of PAP-2 powder billets. The liquid phase forms owing to Al–Al4C3 eutectic melt. The layered structure forms owing to the liquid-phase merging of flaky PAP-2 particles over the contacting planes. The dispersion hardening of the aluminum matrix is achieved thanks to precipitating nanoscale lamellar aluminum carbide crystals from the eutectic melt upon cooling. The synthesis of δ-Al2O3 alumina crystals occurs owing to the interaction between aluminum and residual air oxygen in the course of sintering in the furnace under vacuum at 10–5 mm Hg. It has been found that, under the conditions of static loading, the samples exhibit stable fractures according to a shear delamination mechanism accompanied by cavities appearing when layered blocks are torn out under the action of shear stresses (σbend = 430–500 MPa, K1c = 14.0–15.5 MPa m1/2). Under impact loading, a significant amount of material is involved in the fracture with the formation of cleavage steps between layered blocks and extended zones with ductile-fracture dimples. Due to this mechanism, a high level of KCU (1.1 × 105 J/m2) comparable to the VT-5L titanium alloy is achieved. The developed composite could be used for the manufacture of lightweight structural elements operating under the conditions of dynamic loading.

Phase Transformation Behavior of Lead and Zinc in the High-Lead Slag Reduction Process

Abstract: The phase transformation behavior of lead and zinc in the high-lead slag reduction process was reported in this article. First, the occurrence state of lead and zinc in the slag and the phase transformation behavior of lead and zinc during reduction were investigated. Following, the thermodynamic modeling calculation for the reduction process was constructed and discussed. The results indicated that the zinc in the high-lead slag mainly existed in the form of zinc ferrite and silicate while the lead mainly existed in a silicate form. The XRD patterns of the reduced slag at different coal ratios demonstrated that the lead existing in the high-lead slag in a silicate form could be reduced into the metal phase while the zinc existing in the high-lead slag in the form of zinc ferrite (ZnFe2O4) could be converted into zinc silicate (Zn2SiO4), as the coal ratio increased. The thermodynamic modeling calculation results showed an agreement with the experiment analysis.

Oxidation Properties of W–5% Re and W–26% Re Tungsten–Rhenium Thermocouple Wires

Abstract: Herein, the oxidation properties, i.e., oxidation processes in air, oxidation-product composition, and oxide-film growth, of tungsten–rhenium thermocouple wires were investigated via differential scanning calorimetry (DSC), thermogravimetry (TG), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A tungsten–rhenium thermocouple was protected against oxidation using solidification technology, and the cross sections of the thermocouple wires were observed via SEM. The results showed that the oxidation-initiation temperatures for the W–26% Re and W–5% Re thermocouple wires were ≤681 and ≤873°C, respectively, in air. Moreover, the major oxidization product at high temperature was WO3. The oxide layers were unable to form protective films owing to the generation of stress-induced cracks that grew in radiating lines. The protected tungsten–rhenium thermocouple wires remained intact during oxidation, and oxide layers were not detected.

Novel Method for Producing Chromic Oxide without Hexavalent Chromium Pollution by Acid Leaching

Abstract: Chromic oxide (Cr2O3) is one of the most important chromic salts and is widely used in industrial applications. Traditionally, Cr2O3 is prepared from chromium trioxide (CrO3) or sodium dichromate (Na2Cr2O7), both of which are manufactured from chromite ore. However, traditional manufacturing processes are time-consuming, inefficient, and energy-consuming, and they can catheuse severe environmental pollution by discharging large quantities of solid residues containing Cr in the form of Cr(VI) compounds. These compounds are also harmful to human health. Therefore, developing an environmentally friendly production process is of great concern to the chromic oxide industry. In this study, a new method for producing Cr2O3 without hexavalent chromium pollution was investigated. In this novel process, 97% of the total Cr—in the form of chromium sulfate (Cr2(SO4)3)—and Fe are leached from ferrochrome alloy using sulfuric acid. The concentration of Fe in the Cr2(SO4)3 solution can be reduced to 2 mg/L after precipitating with oxalic acid and extracting with di (2-ethylhexyl) phosphate. Cr2O3 is then produced by precipitating Cr from the Cr2(SO4)3 solution with sodium hydroxide, followed by calcination of the precipitated Cr(OH)3 at 500°C. Using this method, Cr2O3 with a purity of up to 99.3% was obtained in this study. Throughout the process, Cr existed only in the form of Cr(III); thus, the pollution caused by hexavalent Cr was eliminated, and environmentally friendly production of Cr2O3 was achieved.

Structure Formation of Cu–W Pseudo Alloys Upon Various Methods of Their Production

Abstract: This article compares the microstructures of alloys formed upon the sintering of powdered mixtures of tungsten (PV2, average particle size 3.8–6.0 μm) and copper (PMS–11, particle-size fraction 45–60 μm) produced by various methods: the simple mixing of powdered metals, the mechanical activation (MA) of powdered metals, and the deposition of copper from a solution of its sulfate (Cu2SO4·5H2O) on powdered tungsten with simultaneous mechanical activation. The molar ratio in metals in mixtures is Cu/W = 1. The aqueous solution for copper deposition is comprised of diethylene glycol (up to 30%), glycerol (up to 8%), hydrofluoric acid (up to 0.1%), and the OP-10 wetting agent (up to 0.8%). Mechanical activation is carried out in an AGO-2 planetary mill with a drum load of 200 g of steel balls and a drum rotation speed of 2220 rpm for 5 min. Reduced copper in the solution and in air is rapidly oxidized to Cu2O; therefore, the composite powders were washed, dried, and stored in an argon environment. The samples pressed from the powders (tablets with a diameter of 3 mm, height of 1.5–2.0 mm, and density of 7.7–8.0 g/cm3) are sintered in argon at ambient pressure and in a temperature range from 1000 to 1500°C. During the sintering of Cu–W composite particles, it is possible to highlight several regions of the progress of the process. At temperatures below the melting point of copper, solid-phase sintering in the contact points of composite particles occurs. Upon heating from the melting points to 1200°C, the samples from the mixture of powdered metals are sintered according to the liquid-phase mechanism, forming a low porous cake. Sintering of composite powders produced by MA upon copper deposition and the MA of mixtures of powdered metals results in the segregation of samples with the formation of coarse pores extended perpendicularly to the axis of pressing and are partially filled with molten copper. Upon the heating of samples produced by the MA of powders above 1400°C, phase separation occurs and all copper is displaced from the sample to the surface.

Investigation of a Novel CoCrCuNiTi High Entropy Alloy on Microstructure and Mechanical Properties

Abstract: A novel 3d transition metal high entropy alloy (3d TM HEA), CoCrCuNiTi, was exploited by Ti addition into a common 4-elemental group of CoCrCuNi. Its phase constitution, microstructure, and compressive properties in as-cast and annealed conditions were investigated. The studied alloys in both states were composed of a complex multiphase structure, including two BCC phases, one FCC phase, one cubic laves phase, and one HCP Ni3Ti phase. The two BCC phases took up around 50 vol % in total, and the other three phases occurred within the remaining regions. The majority of the BCC phases were attributed to the promising ultimate compressive strength of the studied alloys in both conditions (as-cast: 2.53 GPa, annealed: 2.22 GPa). Furthermore, an outstanding hardness of 694 HV was obtained in the as-cast alloy, implying that no strong relationship was exhibited among the hardness, phase constituent, or valence electron concentration (VEC) in the CoCrCuNi-base HEAs system.